Apparatus in the production of aluminum and other powder with leaf structure or needle form



2,583,456 POWDER ORM N OF ALUMINUM AND OTHER .K. G. WINQUIST ODUCTI WITH LEAF' STRUCTURE OR NEEDLE F Filed Feb 27 1947 APPARATUS IN THE PR Jan. 22, 1952 Patented Jan. Z2, 1952 APPARATUS 1N` THE PRODUCTION `onimu- MTNUM AND oTnEitPownER WITH LEM` STRUCTURE on NEEDLE FORM Karl Gustaf Winquist, Stockholm, Sweden, assignor to Carlfors Aktiebola'g, Hus'kva'rna, 'Sweden, a `,inuit-stock company of'SweTlen Application February 27, 1947, Serial No. 731,272

In Sweden January 1`1, 1946 3 Claims.

-In the "manufacture of porous concrete, socalled gas concrete or light ('pumice-ston'e') concrete, use is made of aluminium powder which, on admixture in the concrete, develops Ehydrogen gas. This process, for simplicitys sake, is often termed fermentation l lculties in the production of such light concrete consists inthep'robl'em of obtaining an aluminlum powder with the desired fermentation period, so thatthe fermentation is completed at the moment when lthe hardening of the concrete begins. The fermentation period is regulated, inter alia, by the size of the particles in the aluminium powder.

Hitherto the sizeof the `particles in the'powder has "been regulated by ordinary sifting through a sieve strainer or the like. The result, however, has notualways been satisfactory, because in this waysifting `according to the weight of the grains as well as the size of their surface area isnot simultaneously attained. The particles of aluminium powder have a leaf-structure, i. e. they consist `of thin metallic flakes. The fermentation period is inversely proportional to the specific surface of the grains, i..e. to the ratio between the surface` area (which is mainly determined by the lengthwise extension) and the Weight of each individual grain. The larger this specic surface, the shorter the vfermentation period. At the-Same time, however, due regardmust be paid to the consideration that the individual grains Shall notA fall below a certain size, asl the pores produced in the eas concrete would then be unduly small, which, of course, is not desirable. the aluminium powder, besides having a certainspeoiiic surface, must also have a certain minimum size of grain, if the desired result is to be attained. These desiderata, which previo usly have not been taken into due account, are not subserved with the hitherto usual methods of sifting aluminium powder.

`The main object of the present invention is to ful-lil then above-mentioned conditions by dividing the powder into suitable fractions, inthe first place according to thespecic surface of the par'- ticles, .=a.nd secondly according to their size.`

Qneembodiment, of an apparatus for performl.the inventionis illustrated in the accompanying drawingv diagrammatically Figure l shows the apparatus, partly in secligure 2, a diagram illustrating the technical improvement gained bythe inventioni [the drawing, `Figure l, 4 denotes 1a fan hav-v nmanlllileliOpening; 'tdwhich a` piping 20 is One of the greatest dif- 2 connected. Into `this #piping unsiitedpowder is fed from acontainerll. `Alongwith a gas stream in which `the powder is mingled, the latter is `carriedby the action fof the fand to an annular chamber 9, into which the gas streamwith the powder is introduced tangential1y.. Here those particles which have -a small specific sur-face as wellas the heavier particles are separated by centrifugal force and lare thrown against the -outer surface of the-annularichamber, iromlwhichthey fall into a funnel-shaped outlet and thence down into a container `E. `Biogas `stream :and those lighter particles which also have alarge specific surface pass -in helical or 'spiral paths through a low` sifting chamber 8, the centre of which is connected witha tube 2|,fserving-a's -an outlet 'tor the gasfs'tream mingled with sifted powder. Thetsaid Vtube2l leads to` a filter 3, `in which the gas is. freed from the sifte'd particles., which fall onto the bottom of the lter and .into a container 'l situated below it. From the lter 3 the purified gasstream .passes through a. tube 22` back to the fan 4.

A conduit 5, which Vat itsone .end is connected l' to the high-pressure side of the fan 4 and `is provided with an adjustable valve 23, leads direct tothe annular chamber 9. `Through this conduit additional gas is supplied to the said chamber, thereby affecting the tangential velocity of the main gas stream carried through thepiping 20 to the chamber, and mingled with unsi'ited powder. Th-us, by 'adjusting `the valve 23, the sifting capacity ofthe apparatus can be regulated.

The air wholly or partly enters tangential-ly an annular cham-bere andllows through '1a low sifting-space `8 between. plane surfaces and the concentric Joutlet, whereupon `the air escapes through a. 'conizluit `2l `in. which the speed of the air can be measured. -`iLli-rmay also enter through a second inlet -5 with avalveiZS-into theann-ular chamber. Thelquantity 1of air in the sift is'ad'- justed toa constant value which is checked by measurement in the tube i8. Thus, the tangential `speed in the inlet will vary 'according to the quantity of ai-'r supplied through thewvalve 23. The `radial speed `is constant because the total quantity of`air ismaintain'ed constant. The airspiral arising-in the plane .sifting space will become more steep upon supplying air through the valve 23. Theresistance in the apparatus is highest when the tangentialspeed is greatesti. e., when the whole quantity of air is `supplied tangentially through thecohduit 2D. The powder `to be sifted is supplied `tothe tangential Jair stream and is dstirbuted uniformly in thexannular cham- 4, 3 ber due to the whirling action. In the inlet of the sifting space in which the powder is introduced into the air spiral by means of the air the powder will be classified so that a smaller portion will be brought together with the air streaming in a spiral path out through the outlet While the greater portion will return to the annular chamber 9 and from this chamber the powder will drop to a collector 2 and the container 6. The necessary control is effected by the valve 23.

During the operation of the centrifugal ventilator strainer not only are the light particles separated from the heavier ones, but also theV grains which have a small surface area are separated from the larger ones. By regulating the velocity or amount of theair, respectively, in the two inlets of the centrifugal ventilator, precisely the desired fraction in regard to specic surface and optimal size of particle can be obtained.

The technical improvement effected by the invention is illustrated by the graph in Figure 2, where the fermentation period in minutes is plotted along the absclssa and the so-called fermentation level in mlllilitres of hydrogen gas is plotted along the ordinate. The curve A represents an aluminium powder produced in accordance with methods hitherto in use, and the curve B an aluminium powder sifted by a centrifugal ventilator in accordance with the invention. Whereas the total fermentation period according to curve A is 27 minutes, according to curve B it is merely l2 minutes. The specific surface of powder A was found to be 4360 cm2, that of powder B 9l00,cm.2, per gram. If a fraction lying between 40.06 and 0.09 mm. is sifted out of eachV of the powders, the-specific surface of the fraction.

out of powder A will be 3940 cm.2 per gram, that of powder B 4900 cm?. The ratio between the thickness of the flakes and their lengthwise extension is 1:37 for powder A, for powder B 1:46.

Seeing that the fermentation rate is inversely of powder B. The specic surface would indeed be increased in this way, but the individual grains would be too small to enable the desired size of the pores in the concrete to be obtained. The proper conditions in both these respects ycan be attained only by centrifugal wind separation.

. The lightest fraction separated in the centrifugal ventilator is sucked out through the discharge outlet and is preferably collected in a filter, e. g. a cloth filter. It has been found that in the sifting of" bronze powder it is very difficult to obtain a tight filter which does not get blocked by dust, thus causing abnormal rise of pressure in the ap` paratus. If, on the other hand, the lter material is less tight, considerable losses of powder will ensue. amounting even in the case of relatively for this powder., which first passes through the 4 i'llter, but gets `caught in it on its next passage. In this way a higher Iconcentration of the powder is obtained in the sifting air, which, however, involves certain risks in regard to inammability.

For this reason,v it is desirable to use-an indiiferent gas, such as CO2, when the risk of explosion will be practically eliminated.

The invention is not limited to its application for aluminium powder, but may be used, for any other metallic powder of leaf or needle structure, or else for graphite, mica or the like. Moreover, it is not restricted to powder for the production of porous concrete, but may also be used with advantage in the production of bronze powder for painting. In that case it ls of considerable importance that it should have a high coating capacity, as in that case a smaller amount of powder will, of course, be consumed. At the same time it is not desirable unduly to diminish the lengthwise extension of the powder particles. as the bronze would then not float up to the surface when dissolved with tincture. Moreover, a largegrained powder will give a higher lustre than ,one with small grains. Y Whenbronze powder is used for coating picture frames or the like, a particularly fine powder withoutlarge and thick particles is desired, as, when the framesare being polished, individual larg-e grains may scratch the surface, thus spoiling the work. In this respect too a veryconsiderable improvement is attained byY centrifugal wind separation.

What I claim is: Y

l. An apparatus for sifting powder comprising in combination a centrifugal wind separator having a narrow sifting space formed between two parallel disks, an annular chamber surrounding said disks and forming a circular inlet to said sifting space, a tangential inlet to said annular chamber, a radial inlet to said annular chamber, said radial inlet Ybeing formed between one of said disks enclosing said sifting space and a third disk parallel thereto, said third disk being provided with a central aperture to which a conduit is connected for supplying a gas stream to said radial inlet, an adjustable valve in said conduit, pumping means for pumping a gas stream through said inlets into said chamber, means'for introducing powder into said tangential inlet and mingling said powder into the gas flowing therethrough, an outlet for powder particles having a specific surface (surface area per unit of weight) less than a predetermined value and a weight greater than a predetermined value, said outlet being connected to the periphery of said annular chamber and directed downwardly therefrom, a further outlet-for the gas stream with the rest of the powder suspendedltherein connected to a central aperture in the upper one of said, disks, and a lter connected to said last mentioned outlet for separating the ,rest of the powder from said gas stream. v

2. An apparatus for sifting powder comprising in combination a centrifugal wind separator having a narrow centrifugal sifting space formed between two parallel disks, an annular chamber surrounding said disks and forming a circular inlet to said sifting space, a circular inlet to said annular chamber, means for introducing a'gas stream together with suspended powder through said tangential inlet to said chamber. a radial inlet to said sifting space, said radial inlet being formed between one of said disks enclosing said sifting space and a third disk of substantially equal size as, said first mentioned` disk and parallel to the same, said third disk being provided with a central aperture, a conduit connected to said central aperture for supplying a gas stream to said radial inlet, an adjustable Valve arranged in said conduit, a centrifugal pump the pressure side of which is connected to said tangential inlet and to said conduit for introducing gas streams thereto, an outlet for powder particles having a specific surface (surface area per unit of Weight) less than a predetermined value, said outlet being connected to the periphery of said annular chamber and directed downwardly therefrom, a further outlet for the gas stream with the rest of the powder suspended therein connected to a central aperture in the upper one of said disks, and a filter connected to said last mentioned outlet for separating the rest of the powder from said gas stream.

3. An apparatus for sifting powder comprising in combination a centrifugal wind separator having a narrow centrifugal sifting space formed between two parallel disks, an annular chamber surrounding said disks and forming a circular inlet in said sifting space, a tangential inlet to said annular chamber, means for introducing a gas stream together with suspended powder through said tangential inlet to said chamber, a radial inlet to said sifting space, said radial inlet being formed between one of said disks enclosing said sifting space and a third disk of substantially equal size as said first mentioned disk and parallel to the same, said third disk being provided with a central aperture, a conduit connected to said central aperture for supplying a gas stream to said radial inlet, an adjustable valve arranged in said conduit, a centrifugal pump the pressure side of which is connected to said tangential inlet and to said conduit for introducing gas streams thereto, an outlet for powder particles having a specific surface (surface area per unit of Weight) less than a predetermined value, said outlet being connected to the periphery of said annular chamber and extending downwardly therefrom, a further outlet for the gas stream with the rest of the powder suspended therein connected to a central aperture in the upper one of said disks, separating means connected to said last mentioned outlet for separating remaining powder from. said gas stream, a conduit leading from said separating means to the suction side of said centrifugal pump, and an outlet for separated powder from said separating means.

KARL GUSTAF WINQUIST.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,761,627 Hine June 3, 1930 1,807,891 Bottcrff June 2, 1931 1,897,144 Prouty Feb. 14, 1933 1,954,117 Caldwell Apr. 10, 1934 2,001,184 Cuppy May 14, 1935 2,087,645 Herman July 20, 1937 2,328,240 Wiegand Aug.. 31, 1943 2,433,178 Ware Dec. 23, 1947 FOREIGN PATENTS Number Country Date 401,630 Great Britain Nov. 16, 1933 628,291 Germany Apr. 1, i936 506,488 Great Britain May 30, 1939 513,834 Great Britain 1939 544,397 Great Britain Apr. 10, 1942` 

1. AN APPARATUS FOR SIFTING POWDER COMPRISING IN COMBINATION A CENTRIFUGAL WIND SEPARATOR HAVING A NARROW SIFTING SPACE FORMED BETWEEN TWO PARALLEL DISKS, AN ANNULAR CHAMBER SURROUNDING SAID DISKS AND FORMING A CIRCULAR INLET TO SAID SIFTING SPACE, A TANGENTIAL INLET TO SAID ANNULAR CHAMBER, A RADIAL INLET TO SAID ANNULAR CHAMBER, SAID RADIAL INLET BEING FORMED BETWEEN ONE OF SAID DISKS ENCLOSING SAID SIFTING SPACE AND A THIRD DISK PARALLEL THERETO, SAID THIRD DISK BEING PROVIDED WITH A CENTRAL APERTURE TO WHICH A CONDUIT IS CONNECTED FOR SUPPLYING A GAS STREAM TO SAID RADIAL INLET, AN ADJUSTABLE VALVE IN SAID CONDUIT, PUMPING MEANS FOR PUMPING A GAS STREAM THROUGH SAID INLETS INTO SAID CHAMBER, MEANS FOR INTRODUCING POWDER INTO SAID TANGENTIAL INLET AND MINGLING SAID POWDER INTO THE GAS FLOWING THERETHROUGH, AN OUTLET FOR POWDER PARTICLES HAVING A SPECIFIC SURFACE (SURFACE AREA PER UNIT OF WEIGHT) LESS THAN A PREDETERMINED VALUE AND A WEIGHT GREATER THAN A PREDETERMINED VALUE, SAID OUTLET BEING CONNECTED TO THE PERIPHERY OF SAID ANNULAR CHAMBER AND DIRECTED DOWNWARDLY THEREFROM, A FURTHER OUTLET FOR THE GAS STREAM WITH THE REST OF THE POWDER SUSPENDED THEREIN CONNECTED TO A CENTRAL APERTURE IN THE UPPER ONE OF SAID DISKS, AND A FILTER CONNECTED TO SAID LAST MENTIONED OUTLET FOR SEPARATING THE REST OF THE POWDER FROM SAID GAS STREAM. 